A variety of data systems depend upon accurate time synchronization for arrangement, correlation and interpretation of data streams pooled from multiple sources or a single source. Accurate time-stamping of the independently collected sensor data streams is often necessary in order to correlate individual data elements. The data acquisition system may be a semiconductor manufacturing system, a large network enterprise, a Global Positioning System (GPS), an automotive system, a vibration analysis system, an optical system, or any other system including at least one sensor. Keeping consistent time across a data system is a necessity for many applications, as illustrated by the following example.
In a vibration analysis system including multiple vibration sensors, each sensor transmits data via cable to a central processor. The central processor receives the data, time-stamps the data, arranges the data according to the time-stamps, and interprets the data to derive a vibration profile. In this example, each vibration sensor is coupled to a separate cable, each cable having a different length. Therefore, by the time the vibration sensor data travel through the cables of unequal length and reach the central processor, the data packets are out of time sequence, thereby corrupting the results of the vibration analysis.
Multiple data collection platforms and multiple data sensors for Air/Ground/Space assets are non-synchronous and cannot support synchronous communication. Thus, large volumes of independent data cannot be easily and/or accurately correlated. Extensive engineering effort is typically required to correct for unavoidable phase delays and time errors.
Uncertainties caused by atmospheric fluctuations, transmission medium variations, electromagnetic interference (EMI), and intentional jamming disrupt the quality of the transmission and further degrade the time accuracy which cannot be modeled. Furthermore, timing standardization is difficult or impossible to achieve due a wide variety of timing circuits, equipment manufacturers, and hardware configurations.
The Defense Advanced Research Projects Agency (DARPA) is currently developing a solid-state atomic clock having a volume less than 0.1 cm3 that consumes only a few milliwatts of power. By using micro-electro-mechanical systems (MEMS) chip fabrication technology, it is now possible to produce a miniaturized atomic clock. The atomic clock is fabricated using micro fabrication techniques and is mounted on a standardized integrated chip package. This so called chip scale atomic clock (CSAC) consumes very little power, runs independently, and is expected to be relatively inexpensive compared to the exorbitant price of a larger atomic clock. Once synchronized, the chip scale atomic clock has an accuracy based upon hyperfine transitions of the Rubidium-87 atom, (for example).